Tempering bent glass sheets

ABSTRACT

An apparatus for tempering a bent glass sheet is disclosed. The apparatus comprises means for conveying the sheet through the apparatus and a pair of blastheads for quenching the sheet with quench gas. Each blasthead comprises a plurality of spaced elongate plenums for supplying quench gas to an array of quench nozzles, the nozzles being mutually inclined to provide diverging jets of quench gas. The plenums extend transversely to the direction of conveyance of the sheet, and the array of nozzles is curved in at least one direction. The array may comprise rows of nozzles extending along lines which are curved in the direction of elongation of the plenums; preferably the curvature of the rows matches the average local curvature of the bent glass sheet in the corresponding direction. Also disclosed is a production line incorporating the apparatus.

This application is the U.S. National Stage Application under 35 U.S.C.§371 of International Application No. PCT/GB2004/001263, filed on Mar.25, 2004 designating the U.S., and claims priority under 35 U.S.C. §119with respect to European Application No. 03425197.5, filed on Mar. 28,2003, the entire contents of both of which are hereby incorporated byreference.

The present invention relates to an apparatus and method for temperingbent glass sheets, and more particularly to such an apparatus and methodin which a bent glass sheet is tempered by quenching it with jets ofquench gas. The apparatus comprises a means of conveying the sheet alonga predetermined path through the apparatus, and a pair of blastheads forquenching the sheet with jets of quench gas, the blastheads comprisingupper and lower blastheads arranged in opposed relationship above andbelow the predetermined path, each blasthead comprising a plurality ofelongate plenums for supplying quench gas to an array of quench nozzlesfrom which the jets of quench gas issue. The bent and tempered glasssheets produced by the apparatus and method of the invention may beemployed as vehicle glazings, in particular as automotive glazings.

WO 99/26890 discloses an apparatus and method for forming heated glasssheets, including a quench station. Insofar as this specification andthe related U.S. Pat. No. 5,917,107 describe the quench station, theyare primarily concerned with a quench station loader for installing aset of upper and lower quench modules.

U.S. Pat. No. 5,273,568 discloses a quench station for quenching aheated glass sheet conveyed on a roller conveyor. The patent addressesdifficulties arising from the obstruction effect of the conveyor rollson the jets of quenching gas and the differing quench configurationswhich this causes for the upward and downward-facing surfaces of theglass sheet.

WO 00/23387 (corresponding to U.S. Pat. No. 6,295,842) discloses a glasssheet quench unit and method for quenching formed glass sheets by quenchgas jets that define a uniformly repeating gas jet impingement pattern.Said pattern is an equilateral triangular pattern providing uniformlyrepeating quench cells of equilateral hexagonal shape distributed overthe formed glass sheet. The resultant product is a quenched glass sheetin which the glass stresses are uniformly distributed in its thickness.The gas jets are distributed from perforated metal strips which are rollformed to the desired curved shape.

Unfortunately, the gas jets produced by this apparatus are poorlydefined, and do not provide good heat transfer unless the perforatedmetal strips are placed very close to the glass sheets, which producesoptical distortion, and gives practical problems in operation.Furthermore, the uniform stresses produced by the uniform quench patternhave been found to yield excessively long splines on fracture, whichresults in the quenched glass sheet not meeting the required safetystandards for vehicle windows.

U.S. Pat. No. 4,515,622 discloses quench apparatus for tempering bothflat and bent glass sheets, the latter being used for vehicle windows.The apparatus comprises opposed blastheads, each including elongatedplenum housings provided with spaced openings which are oriented tosupply angular jets of quench gas towards a heated glass sheet. Theembodiments intended for bent glass sheets (illustrated in FIGS. 5, 6and 8) comprise a glass bending and tempering system including afurnace, a bending station and a quench station. The bending station(designated 62 in FIG. 5) is of the “side exit” type, that is to say,the directions of movement of a glass sheet on entering and exiting thebending station are at right angles to each other. Furthermore, fromconsideration of the elevation view of FIG. 6 in relation to FIG. 5 onwhich it is based, it is apparent that the elongated plenum housingsdesignated 34 are oriented parallel to the direction in which glasssheets advance from the bending station 62 to the quench station 14′.

However, a number of disadvantages are linked to this arrangement.During quenching, the spent quench gas is in part channelled towards thebending station by the plenums. This has the unwelcome effect of coolingthe glass sheet and bending apparatus at a stage in the process where itis critical to maintain the elevated temperature which is imparted tothe glass sheet in the furnace to achieve satisfactory bending andtempering. Indeed, the cooling effect of the quench gas may even extendto the final sections of the furnace, reducing the thermal efficiency ofthe system. Also, as can be seen from FIG. 6 of U.S. Pat. No. 4,515,622,the plenums converge in an upward direction, so that there isconsiderably less space between the plenums of the upper blasthead thanthe lower blasthead. Additionally, the amount of space decreases in anupward direction away from the glass sheet. This arrangement of plenumsmeans that dispersal of spent quench gas (referred to as “air release”for short, as the quench gas is normally air) on the upper side of theglass sheet is restricted, resulting in a less efficient operation.

Moreover, it is inevitable that occasionally a glass sheet will break inthe quench station, and the resulting fragments of broken glass(“cutlet”) must be removed to reduce the risk of scratching ofsubsequent glass sheets passing through the quench station, and eventualblockage of the apparatus. In the apparatus of U.S. Pat. No. 4,515,622,access for removal of cullet from between the plenums is only possiblefrom along the line, i.e. from the upstream side through the bendingstation, or from the downstream side of the quench station, where anunloading station or other apparatus would normally be present. Ineither case access is restricted, and this makes cutlet removal slow andlaborious.

The above disadvantages would still apply to the quench apparatus ofFIGS. 5, 6 and 8 of U.S. Pat. No. 4,515,622 even if it were re-arrangedso that the furnace, bending station and quench were in line with eachother.

It is important to be aware that vehicle manufacturers continue tostrive to reduce the weight of vehicles in the interests of improvedfuel economy, and so interest continues in reducing the thickness of theglazings in the vehicle. This in turn requires that the glassmanufacturer develop techniques for tempering ever thinner bent glasssheets to the requisite international safety standards.

It would be desirable to provide a production line for tempering bentglass sheets, which not only alleviated the disadvantages of the knownapparatus outlined above, but also allowed thinner sheets to be temperedefficiently.

According to the present invention, there is provided an apparatus fortempering a bent glass sheet, comprising a means of conveying the sheetalong a predetermined path through the apparatus, and a pair ofblastheads for quenching the sheet with jets of quench gas, theblastheads comprising upper and lower blastheads arranged in opposedrelationship above and below the predetermined path, each blastheadcomprising a plurality of spaced elongate plenums for supplying quenchgas to an array of quench nozzles from which the jets of quench gasissue, the length of the quench nozzles exceeding their diameter, andthe quench nozzles of each plenum being mutually inclined to providediverging jets of quench gas, characterised in that the plenums extendtransversely to the direction of conveyance of the bent glass sheet andthe array of quench nozzles is curved in at least one direction.

The array of quench nozzles may be regarded as extending over a curvedsurface and comprising rows of nozzles in at least one direction.

Arranging the plenums transversely allows the spent quench gas toexhaust to the sides of the production line, where it has nodisadvantageous effect on other parts of the line. The plenums may thenbe arranged in parallel fashion, enabling better air release.Furthermore, access between the plenums may be had from the sides of theline, facilitating cullet removal. As this invention is solely concernedwith the production of bent and tempered glass sheets (i.e. not flatglass sheets), and it is preferable to bend the glass sheets so that theplane of curvature, or the greater curvature, as the case may be, istransverse to the direction of conveyance, it will be appreciated thatthe rectilinear rows of quench nozzles described in the prior art are nolonger compatible with the desired arrangement of the plenums.Consequently, an important element of the present invention is theprovision of rows of quench nozzles which extend along curved lines, andthe curved lines may be curved in the planes of the plenums (whichinclude the direction of elongation of the plenums) to form athree-dimensional quench. Suitably, the array of quench nozzlescomprises rows of quench nozzles extending along lines which are curvedin the direction of elongation of the plenums. The invention therebyprovides a quench apparatus able to provide three-dimensional quenchingsuited to the bent glass sheets required to manufacture present-dayglazings.

In this specification, the plane of curvature is regarded as being theplane in which the radii of curvature lie, and references to thedirection or orientation of curvature are to be construed accordingly.Complex curvatures may be resolved into curvatures in two planes atright angles to each other.

Preferably, the rows of quench nozzles extend along lines which arecurved to match the average local curvature of the bent glass sheet inthe corresponding direction. Reference is made to “average localcurvature” because it is normal to move a bent glass sheet while it isbeing tempered, and so the jet from a given quench nozzle will impingeon an extended area of the glass sheet, over which the curvature mayvary to some extent.

Alternatively or additionally, the sheet may have a curvature in thedirection of conveyance, and successive plenums in the direction ofconveyance may be arranged so that their profile at the level of thenozzles is curved in the direction of conveyance. In this situation, itis preferable that the profile of the plenums is curved to match theaverage local curvature of the bent glass sheet in the direction ofconveyance.

It is also preferable that the bent glass sheet is oscillated whilebeing tempered. This results in a tempered glass sheet having improvedfracture characteristics.

It will be appreciated that for optimised quenching efficiency, thequench nozzles need to be close to the surfaces of the bent glass sheet.However, when the bent glass sheet has significant curvature in itsdirection of movement, this may render it impossible for it to enterbetween the blastheads. Advantageously, therefore, the blastheads arearranged to be movable towards and away from each other, so that the gapbetween them may be increased. The blastheads may then be moved apart toallow the sheet to enter between them, moved back towards each other toachieve the desired separation for the quenching operation, and thenmoved apart again to allow the sheet to exit from between theblastheads.

If one considers the apparatus to have a centerline parallel to thedirection of conveyance, then, advantageously, successive plenums of thelower blasthead are connected to each other by connecting surfaces whichare inclined away from the centerline. This feature aids cullet removal,as cullet naturally tends to fall outwards from the centerline towardsthe sides of the apparatus under the action of gravity. Preferably,successive plenums of the upper blasthead are connected to each other byconnecting surfaces which are inclined towards the centerline, i.e. inthe opposite direction, so that, if one considers a transversecross-section of the line, the opposed connecting surfaces of the upperand lower blastheads diverge away from the centerline and towards thesides of the line. Spent quench gas exhausts more easily with thisarrangement, because it reduces the back pressure which would otherwisebuild up, and alleviates the recirculation of hot spent quench gas nearthe centerline of the apparatus.

Suitably, the quench nozzles are formed as bores in a nozzle bar, theoutlets of the nozzles being level with a surface of the bar, at leastone such bar being incorporated into each plenum at its face nearest tothe path of conveyance of the bent glass sheet. Preferably the nozzlebores are formed by drilling the bar. It is advantageous for the outletsof the nozzles to be level with the surface of the bar, because the barthen presents a smooth surface towards the glass sheet being quenched,and broken glass is less likely to lodge on such a surface and affectair release or scratch the sheet. Moreover, such nozzle bars are lesssusceptible to damage than, for example, exposed tubular nozzles.

While such nozzle bars may be made of metal, as they commonly have beenin the past, it has been found, surprisingly, that some non-metallicmaterials are also suitable, e.g. certain plastics materials, rubbers ormachinable ceramic materials. Contrary to expectation, heat-resistantplastics materials and rubbers survive in this environment (i.e. despitethe proximity of glass sheets initially at up to 650° C.), because theyare cooled by the passage of quench gas through the nozzles; similarly,the jets of quench gas afford some protection from the abrasive effectof cullet, as they tend to cause cutlet to drop in-between the plenums.Suitable plastics materials are tough, machinable, materials which areheat-resistant to at least 120° C., preferably 150° C. Suitable rubbershave a similar degree of heat resistance. Examples includepolytetrafluoroethene (known as PTFE for short), silicon rubber and amodified nylon sold under the name Eptalon™.

An example of a suitable machinable ceramic is the glass ceramicavailable under the name Macor™ from Corning, Inc. of New York, whichcomprises approximately 55% fluorophlogopite mica and 45% borosilicateglass. It will be appreciated that the hitherto unknown fabrication ofquench nozzles in such non-metallic materials is applicableindependently of the plenum orientation and nozzle configuration, andthus represents an invention which is quite separate from the inventionclaimed in the independent claims of this patent application.

Alternatively, the quench nozzles may take the form of tubes which maybe cylindrical but need not be, conical or part-conical tubes being apossibility among other shapes. Such tubes may be mounted in a bar, orin sheet metal, amongst other ways of affixing them to the plenums.

With regard to the independent claims appended hereto, the inventionalso relates to a method of tempering a bent glass sheet, comprisingconveying the sheet along a predetermined path through an apparatusaccording to claim 1 hereinafter, and quenching the sheet with divergingjets of quench gas,

characterised by conveying the bent glass sheet transversely to thedirection of elongation of the plenums, the diverging jets of quench gasissuing from an array of quench nozzles which is curved in at least onedirection.

According to another aspect of the invention, a production line isprovided for producing bent and tempered glass sheets, comprising afurnace for heating the glass sheets, a bending station, an apparatusaccording to any one of claims 1 to 12 hereinafter, an unloading stationand a means of advancing the sheets along a predetermined path along theline.

The invention will now be further described in terms of the followingnon-limiting specific embodiments, which are illustrated with referenceto the accompanying drawings in which:

FIG. 1 is schematic plan view of a production line for bending andtempering glass sheets, which includes an apparatus for tempering bentglass sheets according to the invention;

FIG. 2 a is a side view of the apparatus of FIG. 1, and FIG. 2 b is adetail from FIG. 2 a, showing a variation in certain aspects;

FIG. 3 is a front view of part of the apparatus of FIG. 2 shown somewhatenlarged;

FIG. 4 is a schematic perspective view of part of the apparatus of FIGS.2 and 3;

FIG. 5 is a cross-section of a small part of the apparatus, the line ofsection being indicated on FIG. 1;

FIG. 6 is a plan view of part of a nozzle bar for use in the invention;

FIG. 7 is a front view of the nozzle bar of FIG. 6, showing a somewhatgreater length of it;

FIG. 8 is a greatly enlarged cross-section of the nozzle bar of FIGS. 6and 7, the line of section being indicated in FIG. 6;

FIG. 9 is a view corresponding to that of FIG. 8; showing a differentembodiment of nozzle bar.

Referring to FIG. 1, a production line 10 for bending and temperingglass sheets 11 is shown in highly schematic form. The line comprises afurnace 12 for heating the glass sheets, a bending station 13, a quenchstation 14 and an unloading station 15. The glass sheets are advancedalong a predetermined path along the line by a conveyor 19, which may bea roller conveyor in whole or in part. Other means of conveying thesheets may be included, such as propelling the sheets while supported ona gas cushion, or a shuttle ring which moves between the bending stationand the unloading station. The direction of movement is shown by arrowA, and is parallel to the centre line 17 of the apparatus. Variations ofthe basic layout of the line are possible; for example, the bendingstation may have one or more side exits, so that the overall line is inthe shape of a letter “L” or “T”, in which case references to theorientation of the plenums should be considered in relation to thedirection of conveyance of the glass sheet through the quench stationitself.

The glass sheets 11 are advanced on conveyor 19 into furnace 12 wherethey are heated to a temperature at which they become heat-softened,thereby enabling them to be deformed, e.g. bent to shape, within atimescale consistent with economic and efficient production.

Each sheet is then advanced into the bending station 13, which in someversions of the apparatus may be positioned within the furnace, or inany case heated to reduce the rate at which the heated glass sheetcools. A variety of bending techniques may be employed to bend the sheetto the desired shape, such as press bending, roll forming or dropforming, or a combination of these, possibly including sag bending.

After bending, the bent glass sheet is conveyed into the quench station14, where it is tempered in an apparatus 16 according to the invention,which is more fully described hereinafter. Finally, the bent andtempered sheet is unloaded in the unloading station 15.

FIG. 2 a illustrates quench apparatus 16 in rather more detail. Theapparatus is viewed from the side of the line 10, and comprises a pairof blastheads for quenching each sheet with jets of quench gas. An upperblasthead 20 and a lower blasthead 21 are arranged in opposedrelationship above and below the path of conveyance through theapparatus. Each blasthead 20, 21 comprises a plurality of spacedelongated plenums 22 which supply quench gas to rows of quench nozzles23 (better illustrated in FIGS. 4 and 6) from which jets of quench gasissue.

Each plenum comprises spaced, generally parallel sidewalls 24 whichextend in their height and width for distances which are large comparedwith the depth of the plenum (the depth being considered as thedimension corresponding to the separation of the plenum side walls).Accordingly, the plenums have the general shape of flat blades or fins.The nozzles are positioned at the lowermost end of the upper plenums,and at the uppermost end of the lower plenums, i.e. the ends adjacentthe path along which the glass sheets are conveyed.

Fans (not shown) supply quench gas, normally air, through ducts (alsonot shown) to the upper and lower blastheads, the air being directedinto the plenums. The air enters the upper blasthead from the top andthe lower blasthead from the bottom. It then passes through the plenums,exits the nozzles and impinges on the bent glass sheet 11 in apredetermined pattern. The bent glass sheet 11 would normally besupported on a quench ring during tempering, but for reasons of claritythis has been omitted from FIG. 2 a (and also FIG. 3).

As already mentioned, this invention relates solely to the tempering ofbent glass sheets, and, as vehicle manufacturers demand ever thinnerglazings for reasons of weight reduction, it is increasingly importantto optimise the heat transfer efficiency of the quench apparatus. Manyvehicle glazings are now specified at a thickness below 3 mm, and highcooling rates are required to temper such thin glazings to the requiredstandard, e.g. ECE R43. As is known in the art, thinner glazings aremore difficult to temper to a given standard than thicker ones, becausemuch higher cooling rates are needed to create the required temperaturedifferential between the surfaces of a glass sheet and its centre, whenthese points are in fact very close together owing to the reducedthickness of thin glass.

Several factors contribute to increased heat transfer efficiency of aquench apparatus. Of course, it is possible to increase the pressure atwhich quench gas (normally air) is supplied, but this requires morepowerful fans, which increase both the capital and running costs of theapparatus. More cost-effective options include optimising quench nozzledesigns, and careful control of the distance travelled by the quench gasbetween exiting the nozzle and impinging on the glass, i.e. theseparation between the nozzles and the glass. Another important factoris the ease with which quench gas can be dispersed after it has impingedon the glass and abstracted heat from the glass surface. Such “spent”quench gas preferably exhausts the apparatus rapidly, and without anyrestrictions which would cause a back pressure to develop. While thesefactors enable thinner glass than previously to be toughened, they arealso advantageous in the toughening of thicker glass, because theincreased quenching efficiency results in cost savings.

The present invention seeks to increase the heat transfer efficiency ofa quench apparatus by exploiting the above factors to advantage, as willbe explained in the ensuing description. As already mentioned, theplenums are arranged to extend transversely of the direction ofconveyance of the bent glass sheets for improved dispersal of spentquench gas. Moreover, measures have been taken to reduce the separationbetween the nozzles and the glass sheet.

A bent glass sheet may be curved in one direction only (cylindricalcurvature) or in two directions at right angles to each other (complexcurvature), where the curvature in one direction may be greater thanthat in the other direction. In either situation, the bent glass sheetmay be conveyed with its curvature, or the greater of its curvatures, asthe case may be, oriented in the direction of conveyance. Successiveplenums in the direction of conveyance are arranged so that theirprofile at the level of the nozzles is curved in the direction ofconveyance. For example, it can be seen from FIG. 2 a that the plenumsvary in height, so that the ends of the plenums which are adjacent thebent glass sheet follow its curvature. The distance between the quenchnozzles 23 and the bent glass sheet 11 may thereby be reduced as much asis possible while still obtaining the desired impingement pattern on thesheet. Pairs of blastheads may be fabricated to match the curvature ofeach glazing to be produced.

It will be appreciated from purely geometrical considerations that, ifthe curvature in the direction of conveyance of a bent glass sheetexceeds the distance between blastheads, it will be impossible for thesheet to pass between the blastheads. A further desirable feature of theapparatus is that the blastheads are arranged to be movable towards andaway from each other. In practice it is simplest to arrange for theupper blasthead to be movable relative to the lower one, and so araising and lowering mechanism 25 is schematically indicated in FIG. 2a.

In FIG. 2 a, a small number of lines 50 have been drawn to represent theposition and direction of some of the jets of quench gas. The plenums 22of the upper and lower blastheads 20, 21 of FIG. 2 a are arranged to bedirectly opposite each other, and opposed quench jets impinge directlyopposite each other onto opposite faces of the glass sheet 11. However,in FIG. 2 b an alternative plenum arrangement is shown for comparisonwith FIG. 2 a, which has certain advantages because of the resultingnozzle configuration.

FIG. 2 b shows parts of a few plenums 22 together with a fragment of theglass sheet 11. The plenums of the upper and lower blastheads are nowstaggered, so that opposed quench jets represented by lines 50 arealigned with each other to be collinear, as are the correspondingnozzles. Once again, opposed jets impinge directly opposite each otheronto opposite faces of the sheet, but this remains the case even if thesheet deviates slightly in the vertical direction from its intendedposition between the blastheads, thus making the quench apparatus moretolerant of slight variations in glass shape or thickness.

FIG. 3 is a front view of the left-hand half of the quench apparatus 16,as seen when looking along the centre line 17 of the line in thedirection of arrow A in FIG. 1. The apparatus has left-right mirrorsymmetry about the centre line, and so the right-hand half correspondsto the left-hand half. It may clearly be seen how plenums 22 are curvedin their direction of elongation, that is to say in a transverse orleft-right direction. Each plenum bears a row of quench nozzles 23extending along a line which is similarly curved in the direction ofelongation of the plenums. A row of nozzles may comprise nozzles ofdifferent orientations (inclinations), or a plenum may bear two rows ofnozzles, one row comprising nozzles inclined in one direction, and theother row comprising nozzles inclined in another direction. As it isdesirable for reasons of air release to keep the space occupied by eachplenum to a minimum, the rows should be close together where twoseparate rows of nozzles are used per plenum.

It is frequently the practice to oscillate the bent glass sheet whilequenching it; the amplitude of oscillation may amount to 1½ times thepitch of the plenums, for example. This means that each jet of quenchgas impinges on an elongate area of the glass sheet, over which thecurvature may vary. Preferably the average local curvature of the line,along which the row of nozzles extends, matches the average localcurvature of the bent glass sheet in the corresponding direction.Rectilinear oscillation of the sheet during quenching generatestoughening stresses in the bent and tempered sheet which arenon-uniform. On fracture, such non-uniform stresses result in anincreased proportion of fracture lines which cross each other,preventing the formation of objectionable long splines which do notcomply with safety standards.

The position and direction of the jets of quench gas are againschematically indicated in FIG. 3 by lines 50. It may be seen that thenozzles and hence jets of the upper and lower blastheads are alignedwith each other also when viewed in the direction of conveyance of theglass sheets. The plenums of each blasthead are connected by inclinedconnecting surfaces 26 which are indicated in FIG. 3, but described inmore detail in connection with FIG. 4 below.

Referring now to FIG. 4, there is shown a schematic perspective view ofpart of the lower blasthead 21. The tops of the plenums 22 are visible,as are the rows of nozzles 23, successive such rows constituting thearray of nozzles referred to above; part of the array 40 is indicated inFIG. 4. It may be seen how successive plenums are connected to eachother by connecting surfaces 26 which are inclined in a downwarddirection away from the centerline 17. The connecting surfaces bridgethe gaps which would otherwise exist between pairs of adjacent plenums.The inclination of the connecting surfaces 26 improves the dispersal ofspent quench gas and aids cullet removal, since gravity naturally causescullet to tend to fall towards the outside of the line. In fact, thecombination of the flow of spent quench gas along surfaces 26, togetherwith the relatively wide spacing of the plenums and the effect ofgravity, may result in such efficient cutlet removal that the blastheadcan be said to be self-cleaning. When selecting the plenum spacing, heattransfer considerations should also be taken into account, as anexcessive plenum spacing would adversely affect heat transfer. Theconnecting surfaces 26 may be planar or curved.

Successive plenums of the upper blasthead are connected to each other bya similar arrangement of connecting surfaces 26 (indicated in outline onFIG. 3), so that the connecting surfaces of the upper blastheadgenerally correspond to those of the lower blasthead when inverted. Thismay be seen from FIG. 3, where parts of the connecting surfaces of bothblastheads are shown in outline. Successive plenums of the upperblasthead are accordingly connected to each other by connecting surfaceswhich are inclined towards the centerline 17. From FIG. 3, it is evidentthat the opposed connecting surfaces of the upper and lower blastheadsdiverge in a generally horizontal direction away from the centerline 17and towards the sides of the line. The volume available for spent quenchgas to exhaust through thereby increases towards the sides of the line,which ensures that back pressure is reduced. Air release, i.e. dispersalof spent quench air, is correspondingly improved.

Referring to FIG. 5, a cross-section of two adjacent plenums of thelower blasthead is shown to illustrate certain details more clearly. Asbefore, the position and direction of the jets of quench gas areindicated by lines 50. These jets issue from quench nozzles 23 (FIGS. 4and 6) which are provided in a curved nozzle bar 51 (FIG. 7). As will beevident from FIGS. 8 and 9, the quench nozzles are mutually inclined,and so the jets of quench gas diverge as indicated by lines 50. Thenozzle bar 51 may be positioned between the sidewalls 24 of the plenum,at the end adjacent the path of conveyance of the glass sheet (i.e. atthe top of the plenums of the lower blasthead, and at the bottom of theplenums of the upper blasthead). The nozzle bar may be positioned whollybetween the sidewalls, as shown in FIG. 5, or it may be provided with alip on each of its long sides, so that it locates on the plenumsidewalls (FIGS. 8 and 9); the latter construction is preferable whenthe nozzle bar is composed of non-metallic, especially plastic,material. A reasonably airtight seal is desirable between the nozzle barand the sidewalls to avoid substantial loss of quench gas. The nozzlebar may be attached to the sidewalls by welding, bonding or riveting,the latter being preferred; rivets 52 are accordingly shown in FIG. 5.

FIG. 6 shows part of the nozzle bar 51 in plan view from above. Quenchnozzles 23 are formed by drilling bores in the bar. Preferably, a singlenozzle bar spans the full width of each plenum, but for fabricationreasons a number of shorter sections of bar may be used to span theplenum, provided that a reasonably airtight seal is achieved whereadjacent sections of bar abut each other. The nozzle outlets areindicated by continuous circles, while the nozzle inlets, which are onthe bottom face of the bar, are indicated by somewhat larger dashedcircles, which are slightly offset with respect to the outlets. This isdue to the chamfering of the inlets, which is described in more detailwith regard to FIG. 8.

FIG. 7 is a front view of slightly more than half of the length of atypical nozzle bar 51. It is symmetrical about the centerline 17, so theother half corresponds. The nozzle bar is curved to match the curvatureof the plenum in which it is fitted. Two nozzles 23 are shown inphantom, although obviously the actual bar is provided with spacednozzles along its entire length.

The nozzle bar may be made in metal, in which case the bar is preferablycut from a block of metal and machined to the appropriate curvature,following which the nozzles are drilled. Alternatively the bar may bemade in a suitable non-metallic material, i.e. one which is heat- andabrasion-resistant, and machinable, such as PTFE or the modified nylonsold as Eptalon™. Such materials are advantageous, not least becausethey can easily be bent to shape to suit the curvature of each plenum.Machining costs are thereby considerably reduced. As mentioned earlier,certain machinable ceramics are also suitable, as are certainheat-resistant rubbers.

FIG. 8 shows a greatly enlarged cross-section of the nozzle bar of FIGS.6 and 7, the line of section passing through a nozzle 23, having aninlet 83 and an outlet 84. The position and directions of the jets ofquench gas are again shown by lines 50 which correspond to the axes ofrespective nozzles; the right-hand line as illustrated indicating thejet which issues from the actual nozzle shown, and the left-hand lineindicating a jet from another nozzle, which is inclined in the oppositedirection to the one shown. Preferably, alternating nozzles are inclinedin opposite directions, and the nozzles of adjacent nozzle bars arealigned, so that the so-called “domino 5” pattern is achieved, i.e. thepoints of impingement of the jets on the glass sheet correspond to thespots on the number five domino piece, repeated over the sheet. That is,the jet impingement points are positioned at the intersections of asquare grid, with a further impingement point at the centre of eachsquare, these further points forming a second square grid overlaying thefirst. This pattern, together with appropriate oscillation of the sheetduring quenching, has been found to yield an optimised fracture patternfor tempered glass. Careful calculation of nozzle position in terms ofpitch, distance from the glass sheet and angle of inclination isrequired in order to produce a regularly repeating impingement patternon the glass, despite varying curvature of the glass and hence thenozzle bar. Nozzle bars of the upper blasthead have tighter radii ofcurvature and smaller nozzle pitches than the bars of the lowerblasthead.

Preferably, at least some of the nozzles have profiled bores. Forinstance, the nozzles may be chamfered at their inlet ends 83, i.e.whereas the bore of each nozzle 23 has a cylindrical section 80 leadingto the outlet 84, it has a conical section 81 leading from the inlet 83,and the transition from one section to the other may be gradual, e.g.the bore may be smoothed to avoid a sharp internal edge. All thesemeasures reduce pressure losses through the nozzles, and hence result ingreater efficiency. An alternative nozzle configuration need not includea cylindrical section at all, the bore comprising a series of conicalsections, in which the angle of taper of the bore (i.e. the anglesubtended at the vertex of an imaginary cone which is tangential to thebore at the point at which the angle of taper is to be determined) mayvary along its length, e.g. from a large taper at the inlet to a smalltaper at the outlet. There may be continuous variation in the angle oftaper along the length of the bore. The lips 82 which locate the bar onthe plenum sidewalls are also visible in FIG. 8, and the outlets 84 arelevel with the upper (as illustrated) surface 85 of the bar, i.e. theydo not protrude from the bar.

The length of the nozzle (as measured along the axis of the bore)exceeds its diameter at the outlet end, and may approach approximatelytwice the diameter. This provides well-defined quench jets, withoutincurring excessive frictional losses, which increase running costs.Well-defined quench jets allow the blastheads to be positioned furtherfrom the surfaces of the glass sheet while still achieving the desiredheat transfer rate and quench pattern. This in turn yields betteroptical quality and makes day-to-day operation of the apparatus easier.

FIG. 9 is a cross-section of an alternative embodiment of nozzle bar 90,the view corresponding to that of FIG. 8. The upper surface 91 of thisbar is arranged, as far as possible, to be perpendicular to the axes 50of the mutually inclined nozzles 92. That is, the upper surface itselfcomprises two mutually inclined surfaces which meet at an apex along thecenterline 93 of the nozzle bar 90. This enables the wall of thecylindrical section 94 to be of identical height around virtually thewhole of the circumference of the bore, thereby providing betterdefinition to the quench jet. Conical section 95 is unchanged, and thenozzle outlets are still level with the upper surface 91 of the bar inthe sense that they do not protrude from it.

Bearing in mind the comments made in connection with FIG. 8 aboveregarding the need for accurately calculated nozzle positions, it hasbeen found in practice that the parameters calculated for suitablenozzle geometries lie within the following parameter ranges:

Inclination of nozzle (to vertical): 7°-20°, preferably 10° to 16°.Diameter of nozzle outlets: 4-10 mm, preferably 6-8 mm. Nozzle pitchalong bar: 15-30 mm, preferably 20-25 mm. Plenum spacing (from centres):30-60 mm, preferably 40-50 mm. Length of nozzle (on axis): 6-16 mm,preferably 9-13 mm.

It has already been explained that the bent glass sheet to be temperedmay have curvature in just one direction, or in two directions at rightangles to each other. While the quench apparatus of the invention may beadapted to handle bent glass sheets in any generally horizontalorientation, it is simpler to align the sheets with their curvature, ormajor curvature as the case may be, at right angles to the direction ofconveyance or centerline of the production line. The sheet will then beflat, or have only minor curvature, in the direction of conveyance. Manyvehicle glazings are elongated in one direction, and it is in fact thecase for certain glazings, e.g. rear windows, that the major curvatureis in the direction of elongation, being so-called “wrap” curvature.Accordingly, for such glazings it is preferable that the means ofconveying the sheet is adapted to convey the sheet in a directionperpendicular to its direction of elongation, and that the direction ofelongation of the plenums 22 is parallel to the direction of elongationof the sheet 11, as illustrated in FIG. 1. The apparatus may also bereadily adapted for other glazings such as side glazings or roofglazings where the major curvature is not necessarily in the directionof elongation.

The invention is applicable both to production lines in which a shuttlering is used to transport the bent glass sheet through the quenchstation, and also to lines in which the bent glass sheet is transportedthrough the quench station on rollers. In the latter case, accountshould be taken of the presence of rollers within the array of quenchnozzles, especially the effect on air release.

1. An apparatus for tempering a bent glass sheet, comprising means forconveying the bent glass sheet along a predetermined path through theapparatus, and a pair of blastheads for quenching the bent glass sheetwith jets of quench gas, the blastheads comprising upper and lowerblastheads arranged in opposed relationship above and below thepredetermined path, each blasthead comprising a plurality of spacedelongate plenums for supplying quench gas to an array of quench nozzlesfrom which the jets of quench gas issue, each plenum possessing alongitudinal centerline extending along a longitudinal extent of theplenum, each nozzle possessing an axis, each plenum bearing one or tworows of quench nozzles, successive such rows constituting the array ofquench nozzles, the length of the quench nozzles exceeding theirdiameter, and the quench nozzles of each plenum being inclined so thatthe axes of some of the nozzles of each plenum are inclined to one sideof the plenum relative to a vertical plane containing the longitudinalcenterline of the plenum and the axes of others of the nozzles in eachplenum are inclined towards an opposite side of the plenum relative tothe vertical plane containing the longitudinal centerline of the plenumto provide diverging jets of quench gas, wherein each of the plenumsextends transversely to the direction of conveyance of the bent glasssheet, thereby affording side access between adjacent pairs of plenums,and each array of quench nozzles is curved in at least one direction,the apparatus possessing a centerline parallel to the direction ofconveyance, and successive plenums of the lower blasthead are connectedto each other by connecting surfaces which are positioned between andconnected to the successive plenums, the connecting surfaces beinginclined downwards away from the centerline.
 2. An apparatus as claimedin claim 1, wherein the one or two rows of quench nozzles constitutingthe arrays extend along lines which are curved in the direction ofelongation of the plenums.
 3. An apparatus as claimed in claim 2,wherein the one or two rows of quench nozzles extend along lines whichare curved to match the average local curvature of the bent glass sheetand are curved in a direction that is the same as the bent glass sheet.4. An apparatus as claimed in claim 1, wherein successive plenums in thedirection of conveyance are arranged so that their profile at the levelof the nozzles is curved in the direction of conveyance.
 5. An apparatusas claimed in claim 4, wherein the profile of the plenums is curved tomatch the average local curvature of the bent glass sheet in thedirection of conveyance.
 6. An apparatus as claimed in claim 4, whereinthe blastheads are arranged to be movable towards and away from eachother.
 7. An apparatus as claimed in claim 1, wherein the quench nozzlesare formed as bores in a nozzle bar, the outlets of the nozzles beinglevel with a surface of the bar, at least one such bar beingincorporated into each plenum at its end nearest to the path ofconveyance of the bent glass sheet.
 8. An apparatus as claimed in claim7, wherein the bores are part cylindrical and part conical, the conicalpart being at the inlet end.
 9. An apparatus as claimed in claim 8,wherein the length of the cylindrical part of the bore is equal to orgreater than the length of the conical part.
 10. An apparatus as claimedin claim 7, wherein the bar is non-metallic.
 11. An apparatus as claimedin claim 7, wherein the bar is composed of polytetrafluoroethene.
 12. Anapparatus as claimed in claim 7, wherein, for each nozzle bar,immediately adjacent nozzles are inclined in opposite directions.
 13. Amethod of tempering a bent glass sheet, comprising conveying the sheetalong a predetermined path through a tempering apparatus, and quenchingthe sheet with diverging jets of quench gas, the bent glass sheet beingconveyed transversely to the direction of elongation of the plenums, andthe diverging jets of quench gas issuing from an array of quench nozzleswhich is curved in at least one direction; wherein the temperingapparatus comprises means for conveying the bent glass sheet along apredetermined path through the tempering apparatus, and a pair ofblastheads for quenching the bent glass sheet with jets of quench gas,the blastheads comprising upper and lower blastheads arranged in opposedrelationship above and below the predetermined path, each blastheadcomprising a plurality of spaced elongate plenums for supplying quenchgas to an array of quench nozzles from which the jets of quench gasissue, each plenum possessing a longitudinal centerline extending alonga longitudinal extent of the plenum, each nozzle possessing an axis,each plenum bearing one or two rows of quench nozzles, successive suchrows constituting the array of quench nozzles, the length of the quenchnozzles exceeding their diameter, and the quench nozzles of each plenumbeing inclined so that the axes of some of the nozzles of each plenumare inclined to one side of the plenum relative to a vertical planecontaining the longitudinal centerline of the plenum and the axes ofothers of the nozzles in each plenum are inclined towards an oppositeside of the plenum relative to the vertical plane containing thelongitudinal centerline of the plenum to provide diverging jets ofquench gas, wherein each of the plenums extends transversely to thedirection of conveyance of the bent glass sheet, thereby affording sideaccess between adjacent pairs of plenums, and each array of quenchnozzles is curved in at least one direction, the tempering apparatuspossessing a centerline parallel to the direction of conveyance, andsuccessive plenums of the lower blasthead are connected to each other byconnecting surfaces which are positioned between and connected to thesuccessive plenums, the connecting surfaces being inclined downwardsaway from the centerline.
 14. A method of tempering a bent glass sheetas claimed in claim 13, comprising moving the blastheads apart to allowthe sheet to enter between them, moving the blastheads towards eachother for the quenching operation, and moving them apart again to allowthe sheet to exit from between the blastheads.
 15. A method as claimedin claim 13, wherein the bent glass sheet is elongate in one direction,comprising conveying the sheet with its direction of elongationperpendicular to the direction of conveyance and parallel to thedirection of elongation of the plenums.
 16. A method as claimed in claim13, wherein the jets of quench gas are arranged to impinge on the glasssheet in a “domino 5” pattern.
 17. A method as claimed in claim 13,wherein the toughening stresses generated in the bent and tempered glasssheet are non-uniform.
 18. A production line for producing bent andtempered glass sheets, comprising a furnace for heating the glasssheets, a bending station, a tempering apparatus, an unloading stationand a means of advancing the sheets along a predetermined path along theline; wherein the tempering apparatus comprises means for conveying thebent glass sheet along a predetermined path through the temperingapparatus, and a pair of blastheads for quenching the bent glass sheetwith jets of quench gas, the blastheads comprising upper and lowerblastheads arranged in opposed relationship above and below thepredetermined path, each blasthead comprising a plurality of spacedelongate plenums for supplying quench gas to an array of quench nozzlesfrom which the jets of quench gas issue, each plenum possessing alongitudinal centerline extending along a longitudinal extent of theplenum, each nozzle possessing an axis, each plenum bearing one or tworows of quench nozzles, successive such rows constituting the array ofquench nozzles, the length of the quench nozzles exceeding theirdiameter, and the quench nozzles of each plenum being inclined so thatthe axes of some of the nozzles of each plenum are inclined to one sideof the plenum relative to a vertical plane containing the longitudinalcenterline of the plenum and the axes of others of the nozzles in eachplenum are inclined towards an opposite side of the plenum relative tothe vertical plane containing the longitudinal centerline of the plenumto provide diverging jets of quench gas, wherein each of the plenumsextends transversely to the direction of conveyance of the bent glasssheet, thereby affording side access between adjacent pairs of plenums,and each array of quench nozzles is curved in at least one direction,the tempering apparatus possessing a centerline parallel to thedirection of conveyance, and successive plenums of the lower blastheadare connected to each other by connecting surfaces which are positionedbetween and connected to the successive plenums, the connecting surfacesbeing inclined downwards away from the centerline.
 19. An apparatus fortempering a bent glass sheet, comprising means for conveying the bentglass sheet along a predetermined path through the apparatus whichfollows a centerline of the apparatus, and a pair of blastheads forquenching the bent glass sheet with jets of quench gas, the blastheadscomprising upper and lower blastheads arranged in opposed relationshipabove and below the predetermined path, the lower blasthead comprising aplurality of spaced elongate plenums for supplying quench gas to anarray of quench nozzles from which the jets of quench gas issue, eachplenum bearing one or two rows of quench nozzles, successive such rowsconstituting the array of quench nozzles, each plenum possessing alongitudinal centerline extending along a longitudinal extent of theplenum, each nozzle possessing an axis, the length of the quench nozzlesexceeding their diameter, and the quench nozzles of each plenum beingmutually inclined so that the axes of some of the nozzles of each plenumare inclined to one side of the plenum relative to a vertical planecontaining the longitudinal centerline of the plenum and the axes ofothers of the nozzles in each plenum are inclined towards an oppositeside of the plenum relative to the vertical plane containing thelongitudinal centerline of the plenum to provide diverging jets ofquench gas, each of the plenums extending transverse to a direction ofconveyance of the bent glass sheet and the plurality of plenums beingarranged in spaced apart relation to one another so that a gap existsbetween adjacent pairs of the plenums to afford side access between theadjacent pairs of the plenums, each array of quench nozzles being curvedin at least one direction, the adjacent pairs of plenums comprising twofirst plenums positioned in spaced apart adjacent relation to oneanother with a first gap between the two first plenums, the adjacentpairs of plenums comprising two second plenums positioned in spacedapart adjacent relation to one another with a second gap between the twosecond plenums, the first plenums being connected to one another byfirst connecting surfaces positioned in the first gap between the firstplenums, the first connecting surfaces extending at an inclinedownwardly away from the centerline to facilitate cullet removal, thesecond plenums being connected to one another by second connectingsurfaces positioned in the second gap between the second plenums, thesecond connecting surfaces extending at an incline downwardly away fromthe centerline to facilitate cullet removal.